1. Field of the Invention
In a common rotary lawnmower design, a cutter blade which is sharpened on opposite edges is mounted directly to a vertical shaft which extends from the crankshaft of an engine. The blade is either rigidly connected to the crankshaft or it is attached by means of a friction assembly which is designed to minimize damage to the blade or shaft when the rotating blade strikes a solid object. However, such friction safety devices do not always operate properly and it is not uncommon for blade shafts to be bent and blades dulled or damaged as a result of the blade striking such an object. Furthermore, the blade frequently becomes clogged with heavy grass, particularly under circumstances when mowing is attempted when the grass is wet. This activity stalls the engine and the grass must then be cleared from the underside of the housing or blade shroud and the blade before restarting the engine. It is well known that both the rigid and frictional drive assemblies are dangerous to the user, since the blade continues to operate unless the object struck is sufficiently solid or heavy to either stop the engine, bend the shaft or blade or engage the friction mechanism.
Due to the ever-increasing number of gasoline powered lawnmowers in use, there has been a growing concern for the danger involved in using both fixed and frictional blade lawnmowers. Since the blade of a fixed or frictional drive lawnmower continues to rotate when the engine is idling, there is always danger of injury, particularly to the feet when the operator is involved in such activity as emptying a grass bag or making adjustments to the lawnmower.
This invention relates to powered lawnmowers and more particularly, to gasoline powered lawnmowers of the rotary design where the operator walks behind and pushes or guides the mower as it operates. A primary object of the invention is to equip such lawnmowers with a reliable clutch and brake apparatus which is operated by a V-belt or chain and is located above the blade shroud or housing and which will quickly and efficiently stop rotation of the mower blade without stopping the engine when the operator releases his grip on a deadman control mounted on or near the handle of the mower.
There have been many attempts to equip rotary gasosline powered lawnmowers with devices which will arrest the rotating blade upon striking an object. These attempts fall basically into two categories, depending upon whether or not the blade is fixed to the drive shaft of the engine. Under circumstances where the blade is driven directly from the engine, release of the deadman control stops the engine immediately. In the second category where the blade is not connected directly to the crankshaft of the engine, the blade is disengaged from the engine and application of a brake terminates rotation of the blade upon release of the deadman control. The common technique of stopping the engine by interupting firing of the sparkplug when the deadman control is released has proved inadequate to stop the blade sufficiently fast to prevent injury from the rotating blade. A time lag of from 4 to 6 seconds between the instant the spark in the sparkplug is terminated and the blade has stopped rotating is not unusual; although the engine is no longer operating, the blade has usually developed sufficient momentum to cause serious injury to the operator or bystander. Another problem which is inherent in this blade braking technique is the inconvenience of restarting the engine before the cutting operation can commence. Because of this inconvenience and because the natural inclination of the operator is to allow the engine to continue running under all circumstances of lawnmowing, there is a great tendency for the operator to deactivate or disengage the deadman throttle control and override the engine-kill safety feature.
Accordingly, the best technique for terminating rotation of a lawnmower blade is to effect not only disengagement of the blade while the engine is continuing to run but also a means for rapidly stopping blade rotation when the disengagement is implemented. Furthermore, the disengaging and blade arrest mechanicsm should be accessible for maintenance purposes and located in a position on the lawnmower where glass clippings and dirt will not impede operation.
The potential for minimizing hazard from injury due to the rotating blade in gasoline powered rotary lawnmowers has received so much attention, that on July 22, 1974, the Consumer Product Safety Commission initiated a proceeding to develop a safety standard for such lawnmowers. On Feb. 26, 1979, this Commission issued a safety standard for powered rotary lawnmowers which requires that all such mowers manufactured after Dec. 31, 1981, be equipped with a deadman control and a blade control system which will accomplish the following objectives: first, prevent the blade from rotating unless the operator activates a blade rotation control; secondly, require continuous contact with the blade rotation control in order that the blade continue to be driven; and thirdly, the blade rotation control must cause the blade to stop within 3 seconds after release.
2. Description of the Prior Art
A "Lawnmower Blade Mounting and Control" is disclosed in U.S. Pat. No. 3,026,665, dated Mar. 27, 1962, to S. J. Hoff. This early Hoff patented device is characterized by an assembly mounted beneath the lawnmower housing and including a depending engine shaft, with a blade mounted by bolts on a hub and rotatably supported on a sleeve bearing carried by the lower end of the shaft. The hub carries a clutch drum having an outer cylindrical wall which stands upward from the upper face of the hub and forms the driven element of a centrifugal clutch for connecting the blade to the shaft. The driving element of the centrifugal clutch includes an assembly which is keyed to the shaft within the clutch drum. A pair of shoes are spring-biased against, and selectively engage the clutch drum such that at rest and at idling speeds, springs retain the shoes in retracted position and the shoes positively engage the drum at predetermined higher speeds. U.S. Pat. No. 4,044,533, dated Aug. 30, 1976, to Gerald H. Wick, discloses a "Lawnmower Blade Clutch and Brake". This device includes a blade housing located beneath the blade housing and supportive for travel over the ground, a drive shaft mounted for rotation by the blade housing and including a clutch drum, an engine connected to the drive shaft and a cutter blade located in the blade housing and mounted for rotation coaxially with and relative to the drive shaft. A clutch shoe is connected to the cutter blade for common rotation therewith and for movement relative to a position of engagement with a clutch drum. A spring urges the clutch shoe into engagement a brake member is movable between a first position where the brake member is spaced from the brake surface, and a second position where the brake member engages the brake surface to brake rotation of the cutter blade and displace the clutch shoe from the position of engagement against the action of the spring. A "Lawnmower Blade Control Apparatus" is disclosed in U.S. Pat. No. 4,148,173, dated Apr. 10, 1979, to Stephen J. Hoff. In this device, a lawnmower blade mounted coaxially at the bottom of a vertical engine drive shaft is normally declutched from the shaft and stopped by a brake responsive to a clutch mechanism located beneath the lawnmower housing. When the engine is accelerated, the blade is released by the brake and clutched by a centrifugal clutch to the engine- driven shaft. The blade carier, clutch and brake drum are included in a compact assembly on a hub and are mounted as a unit on the engine shaft. A flywheel is also included on the hub, and the assembly and flywheel are protected from blade cuttings by a protective bowl shaped to surround the flywheel and form a mounting platform for a brake band which encircles the drum. U.S. Pat. No. 4,205,737, dated June 3, 1980, to Joseph R. Harkness, et al, discloses a "Clutch-Brake Mechanism for Rotary Mower Engines". In this patent, a completely enclosed combination clutch and brake mechanism is permanently mounted at the bottom of a vertical shaft internal combustion engine and is interposed between the crankshaft and a coaxial blade shaft projecting from the bottom of the enclosed clutch and brake mechanism. A cutting blade is fixed to the shaft and a rotatable driving member is attached to the engine crankshaft. A rotatable driven member is fixed to the blade shaft and these members are coupled by radially outwardly movable clutch elements carried by the driven member and frictionalaly engaged with a radially inwardly facing circular surface on the driving member. Springs and centrifugal force cooperate to effect the driving engagement. A "Clutch-Brake Mechanism" is disclosed in U.S. Pat. No. 4,253,556, dated Mar. 3, 1981, to Hugh A. Zindler. The Zindler patent details a clutch mechanism which is operated directly from the crankshaft of a gasoline engine. The mechanism includes segmental clutch shoes which are operatively deployed between coaxial drive and driven members and are movable radially and circumferentially between these members into and out of clutching engagement with a drum located on the drive member. U.S. Pat. No. 4,279,117, dated July 21, 1981, to Randall K. Lawrence, et al, discloses a pair of centrifugally movable shoes pivotally mounted to a blade support in a clutch apparatus which is mounted beneath the blade shroud or housing of a lawnmower. Drive bands are supported by the shoes and are positioned to be engagable with a source of rotational movement, whereby such movement is translated to the blade by the bands, the shoes and the blade support. A brake band selectively engages the shoes to decelerate them and brake the blade. U.S. Pat. No. 4,290,512, dated Sept. 22, 1981, to Hugh A. Zindler, includes a drum carried on the drive member of a rotary lawnmower for driving engagement by clutch shoes carried by the driven member. The clutch shoes are normally biased into driving engagement with the drum and a brake band is utilized to move the clutch shoes out of engagement with the drum and stop rotation of the driven element without interrupting the rotation of the drive member. A "Lawnmower Blade Rotation Warning Device" is disclosed in U.S. Pat. No. 4,297,829, dated Nov. 3, 1981, to Stephen J. Hoff. The subject warning device includes a rotary blade driven from a motor through a centrifugal clutch and normally stopped by a brake which is released by deadman control. The clutch and warning device are mounted beneath the blade shroud of the lawnmower. U.S. Pat. No. 4,326,368, dated Apr. 27, 1982, to Stephen J. Hoff, details a "Clutch and Brake for Rotary Lawnmower" which includes a driving drum and a driven blade carrier, the carrier having clutch shoes engagable with the inside of the drum, and brake drum segments fixed to the shoes and disposed outside the drum for engagement by an encircling brake band. The brake band applies braking drag and additionally serves to mechanically force the segments inwardly to disengage the clutch shoes. The clutching device is mounted beneath the blade housing of the lawnmower.
It is an object of this invention to provide a new and improved clutch and brake apparatus which is indirectly connected to the engine crankshaft by means of a V-belt or chain and is located above the blade housing. The driven component of the clutch and brake apparatus is characterized by a split drum assembly carrying a pair of spring-biased brake shoes and cooperating drum segments pivotally mounted on a hub which is keyed to the drive shaft. The drive element is a pulley drum which rotates freely on the drift shaft when the apparatus is disengaged and is coextensive in alignment with the brake shoes, and clutch disengagement is effected by means of a brake band encircling the drum segments in the split drum assembly to selectively remove the brake shoes from contact with the pulley drum and prevent rotation of the lawnmower blade.
Another object of the invention is to provide a new and improved clutch and brake apparatus which is mounted above the lawnmower housing and is characterized by a shaft provided with a split drum assembly driven element carrying a pair of brake shoes and split drums which are pivotally-mounted on a hub and are spring-biased into contact with a pulley and drum drive component, which pulley and drum are rotatable with the shaft in drive mode to selectively drive the split drum assembly responsive to rotation of the pulley and drum by a V-belt or other drive means. Disengagement and free rotation of the pulley and drum on the shaft is effected by contact between a brake band and the split drums to retract the brake shoes from contact with the drum in the pulley and drum component of the clutch and brake apparatus.
A still further object of this invention is to provide a clutch and brake apparatus which is mounted above the blade shroud or housing of a rotary lawnmower an is operable by belt or chain drive cooperation with an engine to both disengage the drive pulley from the drive shaft and stop rotation of the blade within 3 seconds, responsive to release of a deadman lever or control provided on the lawnmower and linked to the clutch and brake apparatus.
A still further object of this invention is to provide a new and improved clutch and brake apparatus which is indirectly driven by a gasoline-powered engine and is mounted above the blade shroud or housing of a rotary lawnmower and is further characterized by a driven element which includes a split drum assembly pivotally carrying a pair of brake shoes and cooperating-drum segments and a hub keyed to a rotating shaft. A cooperating drive element is characterized by a drive drum and pulley which rotate on the shaft, wherein the brake shoes are normally biased into contact with the rotating drive drum pulley to cause the hub and blade to rotate, and the brake shoes are released from contact with the drum responsive to tightening of a brake band around the drum segments in the split-drum assembly to selectively stop rotation of the blade without killing the engine.